Performance Research On Hydrostatic Lead Screws With Spool-type Restrictors

The screw and nut are the basic function of the key equipment such as CNC machine tools,so many scholars have focused on its structural design and performance analysis.However,the mainstream research are focused on the ball screw nut before.In the recent years,high-speed,overload,high precision,high reliability and other characteristics of CNC machine become the new trend.At the same time,hydrostatic lead screws with its non-Contact transmission,high bearing capacity,high vibration resistance and high precision and other advantages caused the attention of many scholars.As a driving part which convert the rotation of the servo motor to linear motion,Hydrostatic lead screw overcame the shortcomings such as insufficient rigidity,low speed significantly sliding,the repeat precision significantly from the ball screw and complicated control system,poor self-locking ability from the linear motor.However,hydrostatic lead screws drive is not a perfect choice.Hydrostatic lead screws also has its shortcomings:in order to keep pressure,the oil pockets are made on the nut thread surface,which makes the processing more difficult.At the same time,it is difficult to ensure processing accuracy;so in the screw nut thread processing process,it will cause processing error such as pitch error,tooth angle error,tooth width error etc.These processing error will affect the carrying capacity,stiffness,damping and other properties of hydrostatic lead screws.In this paper,it will take static performance into account and design its spool-type restrictors,then analysis the influences of different nut structure parameter and nut pitch error on hydrostatic lead screws static performance.Firstly,I will design the parameters of the screw nut and spool-type restrictors and discuss the influence of different nut structure parameter(such as recess ratio,thread angle,pitch film thickness)on bearing capacity,and do performance comparison between spool-type and capillary restrictors.Secondly,I will analysis the influence of nut pitch error on the static bearing capacity of hydrostatic lead screws.I will establish film thickness model with nut pitch error.According to the principle of hydrostatic,I will establish pressure balance formula and flow rate balance formula,and discuss the hydrostatic bearing performance.Finally,the paper discussed the dynamic pressure effect on the hydrostatic lead screws caused by the nut pitch error.The paper established Reynolds equation and solved it by using the finite difference method and overrelaxation iteration method.Then get the pressure hydrostatic oil pocket and the dynamic pressure distribution on the surface of the oil seal.Simultaneous hydrostatic pressure equation and flow continuity equation,combined with the oil film thickness model with the pitch error,the solution of static pressure oil cavity pressure and dynamic pressure distribution on the surface of the seal oil,and then studied the hydrostatic bearing performance.The research results of this paper have made a reference analysis for the bearing capacity of the hydrostatic screw nut under the influence of the pitch error and different nut structure parameter.It is hoped that has certain reference significance to promote the use of hydrostatic screw nut.